Reductionism is a concept in philosophy that claims a description of properties in a complex system can be "reduced" to the lower-level properties of the system's components. For example, the laws and properties of chemistry can be reduced to the laws of physics.

More specifically, the properties of molecules can be reduced to those of atoms, the properties of biological cells can be reduced to those of molecules, plants and animals can be reduced to those of cells, and mind can be reduced to neurons in the brain.

Beyond the properties, reductionists claim that causal laws of nature in the base level must causally determine the laws of a higher level. These thinkers usually have a highly simplistic, materialistic, and deterministic view of the most fundamental laws of nature, namely the laws of classical physics, or the interpretations of quantum physics that deny indeterminism.

Anti-reductionists deny claims that deterministic causal laws can in principle reduce everything, including life and mind, to the fundamental particles of physics. They include emergentists, who think at least some higher level properties and laws cannot be reduced, but must emerge as sui generis entities that need new explanations. They also include vitalists, who believe that a dualistic, non-physical, immaterial substance is needed to explain life, mind, and consciousness.

This view of the physical world completely ignores energy. The universe was all energy before the temperature declined enough to allow matter to form. And most importantly, this view ignores information, which is neither matter nor energy (though it requires matter for its embodiment and energy for its communication).

The most fundamental tenet of physicalism concerns the ontology of the world. It claims that the content of the world is
wholly exhausted by matter. Material things are all the things
that there are; there is nothing inside the spacetime world that
isn't material, and of course there is nothing outside it either.
The spacetime world is the whole world, and material things,
bits of matter and complex structures made up of bits of matter, are its only inhabitants.

(Physicalism, Or Something Near Enough. Princeton University Press (2005), p.150)

The original reductionists were the ancient Greek materialists, Democritus and Leucippus, who argued that the world consists only of "atoms and the void." But their fellow materialist, Epicurus